TB Micro Flashcards
1
Q
characteristics of mycobacterium tuberculosis
A
- aerobic, acid fast rods
- cell wall has mycolic acid = resistant to detergents and common abx; protects it from desiccation
- grows very slowly on culture
- facultative intracellular
2
Q
TB: transmission, incubation period, virulence factor
A
- transmitted by inhalation
- incubates for 4-12 weeks
- virulence factors = cord factor; gives the bug its characteristic serpentine arrangement
3
Q
what causes the tissue necrosis?
A
immune response
4
Q
what are the symptoms of TB?
A
- mild fever, chest pain, fatigue, malaise, unintentional weight loss
- SWEATING especially night sweats
- PRODUCTIVE cough, sputum could be bloody
5
Q
risk factors for TB
A
- poor nutrition
- drug users
- alcoholics
- crowded living conditions i.e. prison
- immunocompromised
- endemic areas = SE Asia, Sub-Saharan Africa, Eastern Europe
6
Q
3 types of TB
A
- primary TB = initial case
- Secondary TB = reactivation of TB
- Disseminated TB = involves multiple systems AKA miliary TB
7
Q
progression of TB
A
- inhalation of bacteria
- gets engulfed by alveolar macrophages
- the bug isn’t killed; it survives and multiplies
- attracts and activates more macrophages
- forms a tubercle/granuloma in lungs
- can remain dormant for years or decades; something triggers it to come out i.e. becoming immunosuppressed
8
Q
how do the tubercles changes over time?
A
- starts as caseous lesion = cheese like consistency
- becomes Ghon complex = lungs & lymph nodes involved; calcified caseous lesion that shows up prominently on CXR
- then it’s a tuberculous cavities = tubercle that has liquefied & formed an air-filled cavity –> reactivation or miliary TB
9
Q
how can you screen for TB?
A
- tuberculin skin test, Mantoux test, PPD
- intradermal injection of purified protein derivative, check the site in 48-72h, look for CMI
- (+) indicates exposure NOT an active infection necessarily –> type 4 HS rxn
- if the PPD is (+) do a CXR
10
Q
microscopy/culture for TB
A
- acid fast stain or fluorescent auramine stain
- Lowenstein-Jensen agar is specific for TB but very slow growth = 6-8 weeks
11
Q
tx for TB
A
- combo therapy of 4 drugs = isoniazid, rifampin, ethambutol, pyrazinamide
- initial phase = 2 months followed by 4 months of continuation phase
12
Q
what do you give for potential exposure
A
isoniazid treatment
13
Q
what is the main problem with the length of treatment that you have to do for TB? possible solution to the problem?
A
- patient noncompliance is a big problem
- you can do DOTS = directly observed treatment short course i.e. someone watches the pt take their meds every day and if they don’t they can be jailed
14
Q
MDR-TB vs. XDR-TB
A
- MDR = multidrug resistant = resistant to isoniazid and rifampin
- XDR = extremely drug resistant = resistant to isoniazid, rifampin and at least 1 of the 2nd line drugs
15
Q
what is the BCG vaccine and why is it not given in the US?
A
- BCG = Bacille Calmette-Guerin
- live, attenuated M. bovis
- not a high efficacy rate so anyone that gets the vaccine will show a + PPD
- since PPD is what we primarily use to screen in the US if you give the vaccine you lose the effectiveness of your screening test
